The present invention relates to a gear pump of the type which includes a housing for housing gear pump rotors in a housing interior, said housing having a housing end at an end face side of the housing through which at least one pump rotor shaft is guided from the housing interior to the outside. A shaft bearing is arranged in the housing end. In the case of gear pumps of the above-mentioned type, it is known to seal off by means of labyrinth seals rotor shafts which extend to the outside.
Thus, it is known from U.S. Pat. No. 4,336,213 to extend the shaft of a rotor toward the outside for driving purposes. For these purposes, one of the two bearing covers is constructed in two parts. This is usually the axial housing end which is normally screwed to the central part of the housing, viewed in the direction of the rotor axes. The shaft, which extends axially through the cover, enters a separate bearing and sealing part which has a bearing function as well as a sealing function. The receiving bore for the shaft on the bearing/sealing part has a labyrinth seal, that is, a hydrodynamic seal. This type of construction has several disadvantages:
a) The above-mentioned bearing/sealing part or its receiving bore for the shaft, on the one hand, acts as a bearing shell; on the other hand, it acts together with the labyrinth seal as a sealing element along its whole axial section. It is extremely problematic in many of the common types of application or constructions of gear pumps to provide the bearing shells for the rotors with the grooves required for a labyrinth seal; for example, for reasons of surface stress to the screw-shaped contact surface of the bearing shell which, as a result, is increased in a pronounced manner. PA1 b) Obviously, because the manufacturing of the bearing/sealing surface with the integrated labyrinth seal is considered to be so problematic that for this purpose a separate part is provided as the rotation body which is accessible to a relatively easy machining, it is accepted that the bearing cover is to be fastened on the central housing in a sealing manner with the necessity of a corresponding number of fastening anchors, and that, in addition, the cylindrical bearing/sealing part in the bearing cover is to be mounted by means of additional fastening elements, and that additional surfaces are to be sealed, specifically between the bearing/sealing part and the bearing cover.
It is an object of the invention to eliminate these disadvantages. According to the invention, these disadvantages are eliminated by providing a gear pump wherein the shaft bearing is arranged separately from the labyrinth seal at a position spaced axially inward toward the housing interior with respect to the labyrinth seal.
Because of the fact that the bearing of the shaft is arranged in a separate bearing section in the housing axially on the inside and the labyrinth seal axially adjoins the bearing section, a clear separation of functions is achieved for the bearing of the shaft and for the sealing so that the bearing shells can be designed without being impaired by a groove profile and, on the other hand, the labyrinth seal can correspond exclusively to its inherent function, specifically the sealing function.
In contrast to the common assumption that, because of its difficult design, the labyrinth seal is to be provided on a cylindrical bush which is specifically provided for it, which however, requires the acceptance of the above-mentioned problems with respect to the mounting expenditures and the sealing surface, it is further suggested in preferred embodiments of the invention to work the labyrinth seal directly into the shaft receiving opening in the bearing cover.
If, for example, for reasons of wear, it is endeavored in this case to manufacture the labyrinth seal shells of a different material, such as a ceramic material or of special steel, and not of the same material as the housing cover, it is suggested according to preferred embodiments of the invention to provide a bush with the labyrinth seal in the shaft receiving opening on the housing cover by means of pressing, welding or gluing.
A particularly simple solution is achieved according to preferred embodiments of the invention by the fact that the labyrinth seal is worked directly into the wall of the shaft receiving opening on the housing cover.
Furthermore, by developing the gear pump with a cooling duct system in the housing cover, the effect of the labyrinth seal can be adapted to the respective delivered medium.
By designing the housing end as a plate in which the labyrinth seal as well as the bearing section are housed in certain preferred embodiments of the invention, the number of surfaces to be sealed will be reduced further and the flexibility is increased further, for example, with respect to inspections.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.